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Ajp 4 Pot Caliper To 2 Pot


axbol
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Hi folks, does anyone know if it is possible to swap an ajp 4 pot caliper over to a 2 pot caliper. the reason i ask is the front cal on my 2004 beta rev 3 250, is shot. its a bit dear, me being poor, to buy a new one. the 2 pot caliper looks like it will fit, but not sure. i would be happy, i think, with a 2 potter. the 4 pot has been nothing but trouble since i got the bike.

thank in advance..

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When you say 'shot' what do you mean? Unless the metal of the caliper body is damaged, a piston and seal kit will normally be all you need and they are not silly money (I recall about £25). You will of course then be confronted with the spectre of trials bike brake bleeding and expect to question every part of the system, and the parentage of anyone involved in it's design!

However, and this is the big one, bleed it will, and a well bled brake will perform. So, when you say 'shot' do you mean damaged, or just not working well? If you replace the caliper, even with a new one, you will have the same problem; bleeding. So I guess I'm leading to the question, are you absolutely certain the brake is properly bled? If you describe the symptoms, we can try to get to the root cause and prevent you spending any more than you need.

I have written a few quite detailed replies to people struggling with Beta brakes (do a search) as they (and you) all have my sympathy! It took me 2 weeks of patience, working most evenings at it until the final glimmers of firmness appeared!

Graham

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I have the same proplem on my Rev 3. No front brake! I removed the pads last night and they are worn so that won't help matters. My pal who is a bike mechanic is coming round tonight to have a look. I did notice when I was removing the caliper that there was a lot of brake fluid on the disc and pads, upon closer inspection it looks as though the bleed nipple was leaking, I have now tightened this and I hope this was the cause of spongey pressure and naff brakes.

I keep reading about how difficult it is to bleed Beta brakes, I have ridden bikes for years and the brake system looks just like any other, so why would it be such a pain to bleed? I guess I'll find out tonight!

I agree with Graham, swapping to a 2 pot will not be the answer and will only add to your woe's.

Ash

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Ash, I think it's the volume of fluid, both in the system and per lever stroke that makes it hard to shift the air. The rear is a particular problem on Betas because the M/c is on the opposite side to the caliper, so you have a loop where the air can remain trapped. Worse, the banjos oppose so even with the system off the bike it is hard to find an attitude where there isn't an air trap of some form.

When I was at my wit's end with my rear brake, I replicated the system with clear tube and could see an air bubble that never fully made it over the 'hump' in the tube. If you get frustrated and pump like a lunatic, the fluid cavitates and you get froth, making the problem worse! A combination of patience and constantly moving the system around to tease the air towards the bleed nipple eventually prevailed.

BTW, performance tails off hugely when the pads are worn, particularly the rear. I think this is largely down to air again! If there is any at all in the system, the overall increased volume is more affected by heat, and you get more heat back into the caliper when there is less pad material. We often drag the rear too, so we can get the fluid very hot, which will make the brakes spongey...

Graham

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The 4 pots don't like it when the pads wear down, I think if the pistons have to come out that far, they don't come out straight and that's when you get trouble with them jamming up.

I've had one in the past leak, the two halves seemed to have come loose and rocked against each other, squeezing the fluid out of the joint.

Must have been like that a while as no matter how tight, they wouldn't pull up and seal.

I ended up getting the two inner surfaces skimmed flat and fitting a new O ring.

A big one of these

http://www.ebay.co.uk/itm/1-x-100ML-LARGE-DISPOSABLE-SYRINGE-STERILE-/150616229523?pt=UK_HomeGarden_Garden_PlantsSeedsBulbs_JN&hash=item23116d4693

and a bit of tubing attached can be used to back bleed the brake from the nipple.

Just connect it to the nipple, open it and flush the fluid back through the system.

Edited by goudrons
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thanks for the replys folks. the reason i wanna go to a 2 pot is the 4 pot is doing my head in. it got cooked, not by me but my mate. i then replace seals and pistons. it would not bleed for nothing. the pads are fine by the way. so i took the front caliper and put it on the back. it bled perfect in about 10 secs. working fine. i then tried the back caliper on the front, same problems. i am assuming it is warped, even though it looks ok. even swapping pads and pistons and everything else i could think of i have totally give up on it. thats the reason im thinking of a 2 potter up front, i know it wont be as good??? but what the hell, it cant be any worse than the feker i've taken off. once again thanks for all the replys

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When bleeding the front, back off the adjuster where the lever pushes the piston on the master cylinder. The master cylinder has to fully return in order to draw more fluid in from the resovior. The brake can feel spongey even when bled so wind the adjuster in every so often while bleeding to check if the brake goes hard if not wind the adjuster back out and keep bleeding.

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Hi Axbol...I just wrote this up in a new topic:

http://www.trialscentral.com/forums/topic/43089-ajp-brakes-caliper-rebuilding-and-bleeding/

...I probably ought to have looked down the list a litte further before opening a new one. In any case, for what it's worth it documents my bleeding method in good detail. It works for me.

Best of luck...

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cheers for all the advice, especially goudrons about the pads. anyway i must eat some humble pie... i've just replaced the pads with brand new ones, and guess what? thats it, the brake is now working fine. im still confused as to what and why this has happened but hey who cares :wall: . a local bike mechanic told me about pads looking like cheese (wedge shaped) and, to cut a long story short, put brand new in. it has taken 3 weeks of banging my head against a wall and a couple of bottles of brake fluid. so in future my first port of call will be, make sure the pads are fine (new) before stripping everything else down........

axbol

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